Amplifying system



1,524,580 .1. scoT-TAGGART AMPLIFYING SYSTEM Filed Sept. 29 1924Patented Jan. 27, 1925.

UNITED STATES 1,524,580 PATENT oFFlcE.

JOHN SCOTT-TAGGART, OF III'FORID,y NGLAND, .ASSIGNOR T0 ALFREDEB'NESJ..` WHITE,

OF LGNDON, ENGLAND.

AMPLIFYING SYSTEM.

Application led September 29, 1924. Serial N'o. 740,496.

To alt whom t may concern:

Be it known that I, JOHN Scorr-TAGGART, a subject of the King of GreatBritain, residing at Ilford, in the county of Essex, England, haveinvented new and useful Improvements in and Relating to AmplifymgSystems (for which I have filed an application in Great Britain, No.217,971, dated January 2, 1923), of which the following 1s aspecification. I

This invention relates to ampllfying systems, particularly for use inwireless telegraphy and telephony.

It is of general' knowledge that whenv there are employed two or morestages of high-frequency amplification mvolvlng the use of two or morecircuits tuned to the 1ncoming frequency, and arranged so that each oftwo anode circuits has a tuned circuit associated with it either bycoupling or direct-connection, undesirable reactions orself-oscillations will very likely occur. This tendency towardundesirable reactions is due largely to capacity coupllng -in the valvesthemselves.

i It has been proposed to counteract the tendency to self-oscillation ofasingle valve ampliiier due to inherent' capaclty coupling between theelectrodes of the valves by the use of a condenser connected so as topro- -duce a reverse reaction effect, but when a v' plurality of stagesof high-frequency amplication is involved, it has not hitherto beencontemplated, so far as I am aware,

that similar means could be successfully applied to said systems, owingto the relatively greater difliculties involved with each successivestage of amplification. I'v

have found that by the suitable use of condensers connected to pro rterminals of associated inductance coils 1n various stages,

it is possible to neutralize this natural reaction e'ect and therebyinsure the stability of the amplifier.

Accordingly, the invention in part consists of a high-frequencyamplifier in which the currents are amplified by a plurality of stagesof amplification involving a plurality of circuits, one or morecondensers being connected so as to produce a reverse reaction eifect toneutralize the tendency of the amplifier to generate oscillations.

.A further feature of the invent-ion consists in a wireless receiver inwhich the incoming high-frequency currents are ampli- `lied by aplurality of valves in cascade denser, `another and distinct condenserbeing employed to balance out the reaction effects. Y

, Other features of the invention and the methods for carrying the sameinto effect Vwill be seen from a consideration of the preferredembodiment of the same as disclosed in the accompanying drawing, andappended claims.

The diagram shows one circuit arrangement for carrying the inventioninto eilect.

This arrangement as illustrated utilizesv thermionic valves designatedby reference characters' V1 and V2 which serve as hi h frequencyamplifiers, and a third valve which acts as a detector or rectifyingvalve. lach of these valves, as is well known, is provided with afilament, a grid electrode and an anode.l

A source of incoming signals may be a tuned antenna of the 'well knownconstruction. A tuned input circuit coupled to the antenna is connectedto the .grid and to the filament of the valve V1, while the outputcircuit of this valve extends from its anode through the primaryinductance L3, the high tension battery, and thence to the filament. Asis well known, there exists an inherent capacity between the variouselements of each valve, notablyv the grid electrode and anode, which inthe case of the valve V1, is supplemented by the variable condenser C2.The output circuit of the valve V1 is inductively coupledto the inputcircuit connected to the grid of the lValve V2 and to the filament ofthis valve, and includes an inductance L4 shunted by a variable tuningcondenser.

Variable condenser C1 is connected from the grid of the valve V1 to oneterminal of the inductance L, in the input circuit. The

capacity of condenser C1 -is selected with respect to the value of theinherent capacity of the valve V1 and supplemental capacity C2, and isconnected to the terminal of the inductance L, having such a polaritythat the current ilowing through C1 'is equal and opposite in` hase tothe currents owing through the lnherent capacity of the valve V1 and itssupplemental capacity C2.

The output clrcuit of the valve V2 is connected from' its anode throughthe inductance L5 and the high tension battery to the ilament of thisvalve, and the variable condenser C4 is connected between the grid andanode of the valve V2 to supplement its inherent capacity. Theinductance L in the circuit of the valve V2 is inductively coupledthrough the inductance Le to the input circuit of the detector valve V3.In this instance, also, the neutralizing condenser C3, which is similarto C1, is connected from the grid of the valve V2 which it serves toneutralize, to one terminal ofthe inductanceL.

The input circuit of the detector valve V2 is provided with a well-knowngrid condenser and grid leak which need not be described, while .theoutput circuit of the detector valve V3 includes the telephone receiversT or other indicating device 1n series with the high tension battery. Alow tension battery supplies heating current to the filaments of ,thevrespective valves through well known controlling rheostats.

.The natural interelectrode capacity in thermionic valves, such as thatpreviously referred to as existing between the id electrode and theanode,` is usually o an extremely small magnitude, and consequently thebalancing condenser, as for example, C1 or C3, must be correspondinglysmall. A practical ditiiculty is thus introduced both in the mechanicaldesign of such a con denser and in its subsequent adjustment. For theseand other reasons supplemental condensers C2 and C4 have been introducedto increase the natural inter-electrode capacities of these valves to amagnitude which eliminates the aforesaid diiculties. There is frequentlyan appreciable variation in the` inter-electrode' capacities ofprevailing commercial types of thermionic valves and it has been foundthat the association of a supplemental capacity with the inter-elec?frode capacity of the valve may be used to compensate for such variationand provides a convenient means lfor effecting a more practicable andmore readily neutralized inter-,electrode capacity.

Maso

extending between said anode and said lfilament, a transformer havin aprimary winding and a secondary win ing, said primary winding beingincluded in said output circuit, a rectifying device associated withsaid secondary winding, a condenser connecting one end of said secondarywinding of said transformer to said tuned circuit, and a condenserconnected `between said tuned circuit and said anode augment'- ing saidinherent capacity between the grid electric and anode, and saidfirst-named condenser neutralizing the combined capacity of saidinherent capacity plus the augmenting capacity.

'2. An amplifying system embodying a plurality of thermionic valves,each of said thermionic valves havin a grid electrode and an anodebetween whlch inherent ca ac-l ity exists, an input circuit connecte tothe grid electrode, and an output circuit connected to the anode of eachthermionic valve, a condenser supplementing said inherent capacityconnected in parallel there to, and a second condenser, one termin`l ofwhich is connected to the grid electrode of one of said thermionicvalves, the other terminal of said second condenser being connected tothe input ycircuit of another 1 of said thermionic Valves. y Y

An amplifying system embodying a Aplurality "of thermionic valves'ycoupled vin cascade, each thermionic valve being provided with a gridelectrode yand an anode, an arrangement for neutralizing the inherentcapacity existing between the grid elecrtrode and the anode of eachthermionic valve comprising a condenser connected between the gridelectrode and the anode of the thermionic valve in each stage, and asecond condenser connected between the grid electrodes-of the thermionicvalves of successive sta es. I

4. An amp ifying system embodying a plurality of thermionic valves, eachof said thermionic valves being provided with electrodes including agrid and an anode coupled by an inherentv electrostatic capacity, aninput circuit connected to each grid, an outut circuit connected to eachanode, one input circuit being electrically linked to an output circuit,a condenser connected between the grid and the anode of one of saidthermionic valves, a second condenser connected to the grid electrode ofsaid last mentioned valve and to the input circuit of another of saidthermionic valves, and means for adjusting said second condenser so thatthe current flowing therethrough will be equal to and opposite in phaseto the currents owing through the electrostatic capacity and throughvsaid irst' mentioned condenser.

JOHN SCOTT-TAGGART.

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